The “one-number two-terminal” service refers to a user simultaneously using a fixed telephone and a personal handphone system (PHS) (or cellphone) terminal, with the two terminals sharing the same phone number. The fixed telephone and the PHS using the same number can both act as a calling number or a called number independently, and the communication thereof is not affected. When acting as a called number, both of the two terminals may possibly ring, and will ring simultaneously in the simultaneous ring mode. When acting as a calling number, the two terminals can be used independently and if bundled together, the two terminals can call each other. One acts as a primary number and the other acts as an auxiliary number, but to the outside, they are just one primary number. When a user calls this primary number, the “one-number two-terminal” service calls the primary number and the auxiliary number according to certain rules.
A problem occurs in the situation where both terminals are busy in the “one-number two-terminal” service: a user of fixed telephone A subscribes to the “one-number two-terminal” service, its auxiliary number is PHS (or cellphone) B, and its ring mode is simultaneous ringing. If user C calls number A when A and B are in the “busy” state at the same time, user C either can hear the ring-back tone and wrongfully think that the called party is idle at this moment or cannot hear any sound until automatic hang-up a minute later.
The reason for this problem is: fixed telephone A immediately returns a 486 message when “busy”, so that application server AS can immediately learn that fixed telephone A is in the busy state, while PHS (or cellphone) B returns a 183 message when “busy” and then returns a 480 message about a minute later.
If AS mistakes the 183 message of the called party as an idle indication, as shown in FIG. 1, AS sends a 180 idle indication to the calling party upon receiving the 183 message, which causes the calling party to misjudge and think that the called party is idle;
if AS does not process the 183 message, as shown in FIG. 2, then the calling party cannot hear any sound (no prompt at all) during the time the called party returns 183 and 480;
if AS takes 183 as “busy” and hangs up directly, then if PHS (or cellphone) B subscribes to a service such as a ring back tone or a call progress prompt besides “busy”, at this moment, the called party is idle or may be idle, but because AS takes 183 as “busy” and hangs up directly, user C cannot talk to B.
The existing solution is to let the core network carry a Reason header field in the 183 message and send it to AS and map the reason value according to the Q.850 protocol, so that after receiving 183+ reason, the service is able to identify whether this speech path is idle or not via the reason header. This technique requires that the current network switches servers SS with all software docked with the “one-number two-terminal” platform, and supports reporting of message 183 carrying the reason value, and the carried reason value is agreed by the standard or is regular.